Process for the co-production of aromatic carboxylate and alkyl iodides

ABSTRACT

Disclosed is a process for the co-production of aromatic carboxylic esters and alkyl iodides by the carbonylation of aromatic iodides in the presence of an ether and a rhodium catalyst.

This invention relates to a novel carbonylarion process for thepreparation of both aromatic carboxylic esters and an iodine containingcompound from which the iodine values can be economically recovered. Thecarbonylation is conducted in the presence of an ether and a catalyticamount of rhodium.

The carbonylation of aromatic halides in the presence of various GroupVIII metal catalysts to obtain aromatic carboxylic acids and esters iswell known in the art. For example, U.S. Pat. No. 3,988,358 disclosesthe palladium-catalyzed carbonylation of aromatic halides in thepresence of an alcohol and a tertiary amine to produce the correspondingcarboxylic acid ester. Nakayama and Mizoroki [Bull. Chem. Soc. Japan 42(1969) 1124] disclose the nickel-catalyzed carbonylation of aromatichalides in the presence of an alcohol and potassium acetate to producethe corresponding acid ester.

While it is known that aromatic iodides can be carbonylated, the use ofthese materials has been discouraged by the cost associated with thedifficulty of recovering the iodine values. For example, the use ofbasic materials in the carbonylation of aromatic halides, such aspotassium acetate by Nakayama and Mizoroki, results in the formation ofhalide salts from which the halide values can be reclaimed only throughuneconomical procedures involving severe chemical treatments.

In U.S. Pat. No. 2,565,462, Prichard and Tabet disclose thecarbonylation of aromatic halides to aromatic carboxylic esters in thepresence of alcohols, ethers, and phenols using nickel tetracarbonyl.However, only non-catalytic quantities of iron, nickel, and cobalt areused as promoters under reaction conditions of both temperature andpressure that are much more severe than is shown by our invention.

While the literature has been dominated by the use of palladium andnickel as catalysts for the carbonylation of aryl halides, the use ofrhodium as a catalyst is seldom mentioned. One such example is describedby Alper et.al. (Angew. Chem. Int. Ed. Engl. (1984) 732) where amixed-metal rhodium/palladium catalyst is used with an aluminum alkoxidepromoter in the carbonylation of bromobenzene to ethyl benzoate. Thereaction is claimed not to proceed when only rhodium or palladiumcatalysts are used individually. This example also suffers from thedifficulty in recycling halogen values from the aluminum tribromidegenerated in the reaction.

U.S. application Ser. No. 2,521 discloses the carbonylation of aromatichalides to aromatic carboxylic esters and alkyl iodides in the presenceof an alkanol and rhodium. When alcohols are employed in reactions undertypical carbonylation reaction conditions for aryl halides, water is abyproduct. Water can be formed in a number of different ways. Forexample, reaction of in situ generated hydrogen iodide with methanolresults in the formation of methyl iodide and water. Alcohols can oftendehydrate to their corresponding ether and water under typicalcarbonylation reaction conditions. The presence of water in the reactionmixture often leads to the production of a mixture of both carboxylicacids and esters. The presence of acid groups can present a purificationproblem if pure ester is desired as a polymer precursor.

We have discovered a process which not only results in the carbonylationof aromatic iodides to aromatic carboxylic esters with low acid contentin excellent yields and at excellent rates of conversion but alsoresults in production of alkyl iodides from which the iodine values canbe economically recovered. In this invention, the carbonylation isconducted in the presence of an ether and a catalytic amount of arhodium catalyst under aromatic carboxylic ester and alkyliodide-forming conditions of temperature and pressure.

The advantage afforded by our invention over the prior art is two-fold.First, the iodine values in the alkyl iodide may be readily recovered bysimply flashing the relatively volatile alkyl iodide from the mixtureresulting from the carbonylation reaction. This can be accomplishedeither in the carbonylation reactor or, more preferably, in a pressurereduction vessel to which the mixture resulting from the carbonylationreaction is fed. Second, the object in feeding organic ethers is tominimize the amount of water in the carbonylation reactor which willreduce the acid content of the ester product. The ratio of aromaticesters to acids produced in the present invention is dependent on theconcentration of water present in the carbonylation reactor. Thecapability of producing aromatic carboxylic esters with low acid contentis both novel and useful. The low acid content allows for simpler andless expensive production and purification schemes and eliminates theneed for esterification step when esters are the desired product.

The aromatic iodides which may be used in our process may be monoiodo orpolyiodo e.g., di-, tri- and tetra-iodo aromatic compounds. The aromaticnucleus or moiety can contain from 6 to 18 carbon atoms, preferably 6 to10 carbon atoms and may be carbocyclic aromatic such as benzene,biphenyl, terphenyl, naphthalene, anthracene, etc., or heterocyclicaromatic such as pyridine, thiophene, pyrrole, indole, etc. In additionto one or more iodine atoms, the aromatic moiety may be substituted byvarious substituents substantially inert under the conditions employedin our process. Examples of such substituents include alkyl of up toabout 12 carbon atoms such as methyl, ethyl, isobutyl, hexyl,2-ethylhexyl, nonyl, decyl, dodecyl, etc.: cycloalkyl of about 5 to 12carbon atoms such as cyclopentyl, cyclohexyl, 4-butylcyclohexyl, etc.;halogen such as chloro and bromo; alkoxycarbonyl of from 2 to about 8carbon atoms such as methoxycarbonyl ethoxycarbonyl butoxycarbonyl,hexyloxycarbonyl, etc.; carboxyl; cyano; alkenyl of about 2 to 12 carbonatoms such as vinyl allyl, etc.; formyl; alkanoyl of about 2 to 8 carbonatoms such as acetyl, propionyl, butyryl, hexanoyl, etc.; alkanoylamidoof about 2 to 8 carbon atoms such as acetamido butylamido, etc.;aroylamino such as benzamido; and alkylsulfonamide such asmethanesulfonamide hexanesulfonamide, etc.

Specific examples of the aromatic iodide reactants include iodobenzene,1,3- and 1,4-diiodobenzene 1,3,5-triiodobenzene, 4-iodotoluene,4-iodophenol, 4-iodoanisole, 4-iodoacetophenone, 4,4'-diiodobiphenyl,4-chloroiodobenzene, 3-bromoiodobenzene and 2,6- and2,7-diiodonaphthalene. Our process is particularly useful for thepreparation of benzenedicarboxylic and naphthalenedicarboxylic esterswith low acid content and thus the preferred reactants arediiodobenzenes, especially 1,3- and 1,4-diiodobenzene, anddiiodonaphthalenes, especially 2,6- and 2,7-diiodonaphthalene.

The aromatic iodide reactants are known compounds and/or can be preparedaccording to published procedures. For example, T. Hudlicky et.al. TheChemistry of Halides, Pseudohalides and Azides, Supplement D, Part 2,1142-1158, the disclosure of which is incorporated herein by referencein its entirety discloses a number of such processes. Another processdescribed in J. Chem. Soc. 150 (1952) comprises treating an aromaticcompound, such as benzene, with iodine in the presence of silver sulfatedissolved in concentrated sulfuric acid.

The ether used in the process of this invention, which is preferablydimethyl ether, results in the formation of methyl carboxylate esters,which may be used in transesterification reactions, and produces methyliodide which is the most volatile of the alkyl iodides. However, otherethers containing up to about 12 carbon atoms, preferably up to about 4carbon atoms, may be employed if desired. Examples of other suitableethers include diethyl ether, dipropyl ether, dibutyl ether, dipentylether, dihexyl ether, diheptyl ether, dioctyl ether, didecyl ether,dibenzyl ether, dioxane, anisole, or mixed dialkyl ethers. Mixture ofthese ethers may also be employed. For each mole equivalent of aromaticester produced, one mole of ether is required.

The process provided by our invention can also be carried out in thepresence of an organic co-solvent such as aliphatic, alicyclic andaromatic hydrocarbons, and halogenated hydrocarbons. Examples of suchsolvents include benzene, toluene, the xylenes, hexane, heptane,chlorobenzene, ethylene dichloride, methychloroform, naphthalene, etc.However, the use of a co-solvent is not critical to the practice of thisinvention. Water or potential esterifying agents such as alcohols andtheir carboxylate esters may also be present in the reaction mixturedepending upon the desired ester to acid ratio.

The rhodium catalyst can be provided to the reaction medium as eitherrhodium metal or as any of a number of rhodium salts or complexes.Illustrative sources of rhodium are rhodium trichloride, rhodiumtribromide, rhodium triiodide, rhodium acetate, rhodium oxide,dicarbonyl rhodium acetylacetonate, rhodium carbonyl complexes and theirphosphine and halogen substituted analogs. The amount of rhodium is notsignificant as long as enough is present to catalyze the reaction.Preferably, the catalyst is present in a concentration of 10 to 0.001mole percent, preferably 1.0 to 0.01 mole percent based on the moles ofaromatic iodide reactant. Therefore, the total reaction medium has acatalyst concentration of about 10,000 ppm to 10 ppm with preferredcatalyst concentrations of 1,000 to 100 ppm.

The carbonylation reaction is conducted in the presence of carbonmonoxide, which is employed in amounts such that the total reactionpressure is suitable for the formation of both the aromatic carboxylicester and the alkyl iodide. The carbon monoxide employed may beessentially pure or it may contain other gases such as carbon dioxide,hydrogen, methane or other compounds produced by synthesis gas plants.Normally, the carbon monoxide will be at least 90, preferably at least95, percent pure.

The process of the present invention can be conducted at temperaturesand pressures suitable for formation of both the aromatic carboxylicacid and alkyl iodide. The temperatures and pressures are interdependentand can vary considerably. Normally, the pressure will be at least 100psig. While the process can be carried out at pressures as high as10,000 psig, the cost of utilities and equipment required for such highpressure operation may not be commercially justified. Thus, the pressurenormally will be in the range of about 125 to 4,000 psig, preferablyabout 300 to 1,500 psig. A particularly preferred pressure is 500 to1,500 psig. A pressure of 1,200 psig is often most desirable. Whiletemperature as low as 125° C. and higher than 225° C. may be used, ourprocess normally is carried out between about 150° and 275° C. Thepreferred temperature range is 180° to 250° C. A particularly preferredtemperature is 220° C.

The relative amounts of carbon monoxide, ether and aromatic iodide andin our process can be varied substantially and are, in general, notcritical. However, it is preferable to have at least stoichiometricamounts present relative to the aromatic iodide if complete conversionis desired.

When a polyiodo aromatic compound is used as the reactant in ourcarbonylation process, the products obtained include both aromaticpolycarboxylic esters and partially carbonylated products such asiodoaromatic carboxylic esters. The latter compounds are useful asintermediates in the preparation of derivatives of aromatic carboxylicesters, for example, by displacement reactions whereby the iodosubstituent is replaced with other radicals. The difunctional esters,such as dimethyl 2,6-naphthalenedicarboxylate, can be reacted with diolsto produce high molecular weight polyesters suitable for moldingplastics. Useful articles can be molded from these plastics, such as byinjection molding. The relative amounts of partially or totallycarbonylated products is highly dependent on the period of time that thereactant resides under carbonylation conditions.

The alkyl iodides prepared according to the process of our invention maybe used in other chemical processes such as in the preparation ofcarboxylic acids and carboxylic anhydrides according to knowncarbonylation procedures. Alternatively, the alkyl iodide can beoxidatively decomposed at elevated temperature to produce a gaseousmixture of iodine, carbon dioxide, and water from which the iodine canbe recovered. Alternatively, the alkyl iodides may be thermallydecomposed to iodine and an alkane, or hydrogenated to hydrogen iodideand methane.

Our process is carried out at a pKa of less than 5. Therefore, there areno significant amounts of basic materials which preferentially combinewith hydrogen iodide and interface with the formation of an alkyliodide. Examples of such bases which are not present in significantamounts in our process include amines, particularly tertiary amines, andhydroxides, alkoxides and weak acid salts, e.g., carboxylates of thealkali and alkaline earth metals.

Our invention is further illustrated by the following examples. In theprocedures utilized in the examples the materials employed are loadedinto a 330 mL autoclave constructed of Hastelloy B2 alloy which isdesigned to operate in a rocking mode. The autoclave is pressurized with200 psig carbon monoxide gas pressure at room temperature and then thegas is vented and the autoclave is sealed. In Examples 1-8, theautoclave is pressurized to 200 psig with carbon monoxide gas at ambienttemperature and heated and rocked until reaction temperature wasreached, at which time additional carbon monoxide gas is added toincrease the autoclave internal pressure to the predetermined value.Reactor pressure is maintained by adding carbon monoxide at the samerate at which it is consumed by the reactants. The carbon monoxide usedis essentially pure. When the predetermined reaction time is completed,the autoclave is cooled by a stream of cold air to approximately 25° C.After the gas is vented from the autoclave the crude product is isolatedby filtration and analyzed by gas chromatoqraphic methods. The %conversion is the mole percent of iodo-group converted to carboxylicacid or ester. The results are shown below.

    __________________________________________________________________________    Example No.                                                                           1       2       3       4                                             __________________________________________________________________________    Iodoaromatic                                                                          2,6-diiodonaph-                                                                       2,6-diiodonaph-                                                                       2,6-diiodonaph-                                                                       2,6-diiodonaph-                               Wt (g)  thalene thalene thalene thalene                                               30.0    30.0    30.0    30.0                                          Catalyst                                                                              RhCl.sub.3.3H.sub.2 O                                                                 RhCl.sub.3.3H.sub.2 O                                                                 RhCl.sub.3.3H.sub.2 O                                                                 RhCl.sub.3.3H.sub.2 O                         Wt (g)  0.50    0.50    0.50    0.50                                          Ether   Dimethyl Ether                                                                        Dimethyl Ether                                                                        Dimethyl Ether                                                                        Dimethyl Ether                                Vol (mL)                                                                              40.0    40.0    40.0    40.0                                          Co-Solvent                                                                            Naphthalene                                                                           Naphthalene                                                                           Naphthalene                                                                           Naphthalene                                   Wt (g)  100.0   100.0   100.0   100.0                                         Time    1       1       1       1                                             (hour)                                                                        Pressure                                                                              1,500   1,500   1,500   1,500                                         (psig)                                                                        Temp. (°C.)                                                                    190     205     220     245                                           % Conversion                                                                          97.4    100.0   100.0   99.3                                          __________________________________________________________________________    Example No.                                                                           5       6       7       8                                             __________________________________________________________________________    Iodoaromatic                                                                          2,6-diiodonaph-                                                                       2,6-diiodonaph-                                                                       2,6-diiodonaph-                                                                       2,6-diiodonaph-                               Wt (g)  thalene thalene thalene thalene                                               30.0    30.0    30.0    30.0                                          Catalyst                                                                              RhCl.sub.3.3H.sub.2 O                                                                 RhCl.sub.3.3H.sub.2 O                                                                 RhCl.sub.3.3H.sub.2 O                                                                 RhCl.sub.3.3H.sub.2 O                         Wt (g)  0.50    0.50    0.50    0.50                                          Ether   Dimethyl Ether                                                                        Dimethyl Ether                                                                        Diethyl Ether                                                                         Anisole                                       Vol (mL)                                                                              40.0    40.0    40.0    40.0                                          Co-Solvent                                                                            Naphthalene                                                                           Naphthalene                                                                           Naphthalene                                                                           Naphthalene                                   Wt (g)  100.0   100.0   100.0   100.0                                         Time    1       1       1       1                                             (hour)                                                                        Pressure                                                                              1,000   750     1,500   1,500                                         (psig)                                                                        Temp. (°C.)                                                                    220     220     220     220                                           % Conversion                                                                          100.0   100.0   100.0   79.2                                          __________________________________________________________________________

While the invention has been described in detail with particularreference to preferred embodiments thereof, it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

We claim:
 1. A process for the coproduction of an aromatic carboxylicester and an alkyl iodide which comprises carbonylating an aromaticiodide in the presence of an ether and a catalytic amount of a rhodiumcatalyst under aromatic carboxylic ester and alkyl iodide-formingconditions of temperature and pressure.
 2. The process of claim 1wherein the aromatic iodide is selected from the group consisting ofdiiodonaphthalene and diiodobenzene.
 3. The process of claim 2 whereinthe diiodonaphthalene is 2,6-diiodonaphthalene and the diiodobenzene is1,4-diiodobenzene.
 4. The process of claim 1 wherein the ether containsfrom 1 to 4 carbon atoms.
 5. The process of claim 4 wherein the ether isdimethyl ether.
 6. The process of claim 1 wherein the temperature is inthe range of about 150° to 275° C.
 7. The process of claim 6 wherein thetemperature is in the range of about 180° to 250° C.
 8. The process ofclaim 1 wherein the pressure is in the range of 125 to 4,000 psig. 9.The process of claim 8 wherein the pressure is in the range of 300 to1,500 psig.
 10. The process of claim 1 wherein the process is carriedout in the presence of an organic co-solvent.
 11. A process for theco-production of an aromatic dicarboxylic ester selected from the groupconsisting of a dimethyl benzenedicarboxylate and a dimethylnaphthalenedicarboxylate and methyl iodide which comprises carbonylatinga diiodobenzene or a diiodonaphthalene in the presence of dimethylether, an organic solvent and a catalytic amount of a rhodium catalystat a temperature of about 180° to 250° C. and a pressure of about 500 to1,500 psig.
 12. A process for the co-production of dimethyl2,6-naphthalenedicarboxylate and methyl iodide which comprisescarbonylating 2,6-diiodonaphthalene in the presence of dimethyl ether,an organic co-solvent and a catalytic amount of rhodium at a temperatureof about 220° C. and a pressure of about 1,200 psig.